Prior Art
This invention relates to the combination of a solid waste comminuting apparatus and a screening system to divert solid matter contained in an influent stream to the comminutor for purposes of size reduction. Prior screening/comminuting systems are disclosed in U.S. Pat. No. 5,505,388, incorporated here by reference. As set forth in the '388 patent, as is well known in waste water treatment, there are many environments where large volumes of liquid require initial processing for purposes of coarse screening so that large solid objects are diverted in the influent stream and their size reduced by a grinding unit. The material, now of a reduced size, is either removed at the point of reduction or re-introduced into the stream for further processing downstream.
This invention is an improvement over the technology disclosed in U.S. Pat. No. 5,505,388. The '388 patent and the commercial technology stemming from it represented a significant improvement over prior vertically oriented bar screens which were typically used in waste water treatment plants for the purposes of removing solids from a liquid flow. Those prior devices thus utilized rakes, or the like which moved at an angle generally vertical, and therefore perpendicular to the fluid flow in a vertical plane. This resulted in undesirable hydrostatic effects in addition to a propensity of such systems to clog, when fine screens are used, and require a considerable amount of power for purposes of lifting solid materials.
The '388 technology departed from this prior technique by integrating into a common housing a diverter unit, for example a rotating drum placed directly in the fluid flow with an adjacent comminutor disposed in that flow to receive solids that were diverted by the drum. The drum and the comminutor were commonly powered. Consequently, the drum allowed fluid to pass through it but at the same time presented a barrier for solid matter that could not pass through the screening elements. The solid matter was then diverted to one side of the fluid flow where it was then ground into smaller particles and then those particles remain in the stream for substantive downstream processing.
A variant of this basic technique of diverting solids in the stream used double drums, one placed on each side of the comminutor. This system is particular effective for wide flow channels. By this technique, flow rates are maintained in the stream but, solids are efficiently diverted toward the comminutor for size reduction.
These systems have been commercially successful and as a result of that success a number of areas of further improvement have been identified. One area of improvement is in the drive system for the comminutor and the drum. For example it is desirable to incorporate the capability to tighten the stack of the comminutor from the top as disclosed in U.S. Pat. No. 5,478,020. However since the screen assembly and the drive train are located in the top end housing of integrated systems, top stack tightening was not considered to be feasible. Additionally in prior systems rags could wrap around the lowest cutters and combined with grit would degrade the casting material of the end housing. The result was an expensive repair for the entire end housing.
Another area of improvement deals with the diverter and the manner of support. The diverter, typically a drum, employed a side rail on one side to improve flow characteristics and provide structural support. To maintain overall rigidity of the system additional components were required. This was a face plate attached to top and bottom end housings to complete the frame with the side rail. As a part of the frame prior designs used a face plate bolted to the front of the device which served as structure extending the width of the unit. This framing served to mount the overall frame in a sewage channel when it was lowered and secured to a fixed metal structure fastened to opposing walls of the channel. As can be appreciated the face plate is a fixed dimension and mounting was thus a function of channel width and the need to size the framework to match.
Prior designs used a drum having a center shaft running vertically the length of the drum. Small particles of rags and other solids in the waste stream entering the interior of the drum through screen apertures could wrap on the center shaft. Eventually this buildup on the shaft would increase, enlarging in diameter and caused an internal blockage. In turn a loss of flow through the screen could result decreasing the efficiency of the screen.
Previous drum configurations used intermediate sprockets to support the drum in a spatial arrangement along the central shaft of the drum. Any portion of the screen between the sprockets was unsupported except by the interconnection of the screen material itself. This lack of support caused an hour glass effect between the interface of the screen and the grinder. That is the outer surface of the screen parallel to the axis of rotation would not be in alignment causing gaps at the interface with the grinder.
Prior screening systems, for example those described in U.S. Pat. No. 4,919,346 used an internal deflector. This was possible since the diverter was a screen, elongated with two interior shafts. However, in the context of a rotating drum of the type in the '388 patent such internal deflectors could not be incorporated because the diverter was configured around sprockets containing spokes.